This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-175507, filed Jun. 12, 2000; No. 2001-102452, filed Mar. 30, 2001; and No. 2001-171411, filed Jun. 6, 2001, the entire contents of all of which are incorporated by reference.
The present invention relates to a magnetic recording medium and a magnetic recording apparatus.
With improvement in the processing speed of the electronic computer achieved in recent years, a high speed and high-density recording is required for the magnetic recording apparatus (HDD) performing the storing and reproducing functions of information and data. However, the improvement in the recording density is the to be physically limited, and it is doubtful whether it is possible to continue to satisfy the request.
In the case of an HDD apparatus, the magnetic recording medium for recording information comprises a magnetic layer including an aggregate of fine magnetic particles. For performing a high-density recording, it is necessary to diminish magnetic domains recorded in the magnetic layer. In order to discriminate the small recording domains, it is necessary for domain boundaries to be smooth. For making the domain boundaries smooth, it is necessary to miniaturize the magnetic particles contained in the magnetic layer. Also, if the magnetization reversal proceeds to reach the adjacent magnetic particle, the domain boundaries are disturbed. Therefore, in order to prevent an exchange coupling interaction from being produced between the magnetic particles, it is necessary for the magnetic particles to be magnetically separated from each other by a nonmagnetic material. Also, for achieving a high-density recording, it is necessary to diminish the thickness of the magnetic layer in view of the magnetic interaction between a magnetic head and the magnetic recording medium. Under the circumstances, it is necessary to further diminish the volume of the magnetization reversal unit, which is substantially equal to the magnetic particle, in the magnetic layer. However, if the magnetization reversal unit is diminished, magnetic anisotropy energy of the unit, i.e., the product of magnetic anisotropy energy density Ku and magnetization reversal unit volume Va, is rendered smaller than the thermal fluctuation energy, resulting in failure to maintain the magnetic domains. This is the thermal fluctuation phenomenon, which is a main cause of the physical limit of the recording density called thermal fluctuation limit.
In order to prevent the magnetization reversal caused by the thermal fluctuation, it is considered effective to increase the magnetic anisotropy energy density Ku. However, in the case of the HDD medium described above, it is impossible to achieve the recording by the magnetic field that can be produced by the recording head widely used nowadays because the coercive force HCW when the magnetization reversal operation is performed at a high speed, i.e., the recording is performed, is substantially proportional to Ku.
In order to overcome the problems described above, proposed is an idea called thermally assisted magnetic recording. To be more specific, it is proposed to perform the magnetic recording by heating the recording layer in the recording step so as to locally diminish the value of Ku. In this system, the magnetization reversal is made possible by the recording magnetic field that can be produced by the magnetic head widely used nowadays even if the value of Ku of the recording layer is large under the environment in which the recording medium is used, i.e., under ambient temperature in general.
However, since the adjacent track is somewhat heated during the recording step, produced is a cross erase phenomenon that the thermal fluctuation is accelerated in the adjacent track so as to erase the recording domains. Also, since the recording medium is heated to some extent at the time when the head magnetic field is eliminated immediately after the recording, the thermal fluctuation is also accelerated, with the result that it is possible for the domains once formed to disappear.
In order to overcome the problems described above, it is necessary to use a material having as sharp change in Ku relative to temperature as possible in the vicinity of the recording temperature. However, the change in Ku relative to temperature of the CoCr-based and CoPt-based magnetic thin films, which are developed nowadays, is substantially linear, failing to satisfy the requirement pointed out above. It follows that much improvement in track density or linear recording density cannot be expected in the conventional magnetic recording medium.
It is conceivable to increase the value of Va in order to prevent the magnetization reversal caused by the thermal fluctuation. However, if the value of Va is increased by increasing the size of the magnetic particles within the plane of the magnetic recording medium, it is impossible to achieve high-density recording. Also, if the value of Va is increased by increasing the thickness of the recording layer, the head magnetic field fails to reach sufficiently the lower portion of the recording layer. As a result, the magnetization reversal does not take place, resulting in failure to achieve high-density recording.
An object of the present invention is to provide a magnetic recording medium and a magnetic recording apparatus capable of achieving high-density recording exceeding the thermal fluctuation limit.
According to a first aspect of the present invention, there is provided a magnetic recording medium, comprising a substrate; a base layer formed on the substrate and comprising a magnetic material; a switching layer formed on the base layer and comprising a nonmagnetic material; and a recording layer formed on the switching layer and comprising magnetic particles and a nonmagnetic wall buried between the magnetic particles; wherein the medium meets the following condition: TcB greater than Tsw, where TcB is a Curie temperature of the base layer, and Tsw is a temperature at which the recording layer and the base layer begin to exert exchange coupling interaction.
The magnetic recording apparatus using the magnetic recording medium according to the first aspect of the present invention comprises the first magnetic recording medium, a heater locally heating a part of the magnetic recording medium, and a magnetic head applying a magnetic field to the magnetic recording medium.
It is preferable to perform heating and magnetic field application using the apparatus according to the first aspect of the present invention in a manner to meet the conditions of Tw greater than Tsw and TcB greater than Tsw, where Tw denotes a recording temperature of the locally heated recording layer, TcB denotes a Curie temperature of the base layer, and Tsw denotes a temperature at which exchange coupling interaction begins to be exerted between the recording layer and the base layer.
According to a second aspect of the present invention, there is provided a magnetic recording medium, comprising a substrate; a base layer formed on the substrate and comprising a material that is nonmagnetic under an ambient temperature and becomes ferromagnetic at higher temperature; and a recording layer formed on the base layer and comprising magnetic particles and a nonmagnetic wall buried between the magnetic particles; wherein the transition temperature Tf from nonmagnetic to of the base layer is made to be higher than a reproducing temperature.
The magnetic recording apparatus using the magnetic recording medium according to the second aspect of the present invention comprises the second magnetic recording medium, a heater locally heating a part of the magnetic recording medium, and a magnetic head applying a magnetic field to the magnetic recording medium.
It is preferable to perform heating and magnetic field application using the apparatus according to the second aspect of the present invention in a manner to meet the condition of Tw greater than Tf, where Tw denotes a recording temperature of the locally heated recording layer, and Tf denotes a nonmagnetic-to-ferromagnetic transition temperature of the base layer.
According to a third aspect of the present invention, there is provided a magnetic recording medium, comprising a substrate; a base layer formed on the substrate and comprising a magnetic material; and a recording layer formed on the base layer and comprising magnetic particles and a nonmagnetic wall buried between the magnetic particles; the base layer and the recording layer being stacked to exert exchange coupling interaction, wherein structures of the base layer and the recording layer are set to meet the following condition: |TcBxe2x88x92Tw| less than 100K, where Tw is a recording temperature of the locally heated recording layer, and TcB is a Curie temperature of the base layer.
The magnetic recording apparatus using the magnetic recording medium according to the third aspect of the present invention comprises the third magnetic recording medium, a heater locally heating a part of the magnetic recording medium, and a magnetic head applying a magnetic field to the magnetic recording medium.
It is preferable to perform heating and magnetic field application using the apparatus according to the third aspect of the present invention in a manner to meet the condition of |TcBxe2x88x92Tw| less than 100K, where Tw denotes a recording temperature of the locally heated recording layer, and TcB denotes a Curie temperature of the base layer.
According to a fourth aspect of the present invention, there is provided a magnetic recording medium, comprising a substrate; a base layer formed on the substrate and comprising a magnetic material; a switching layer formed on the base layer and comprising a magnetic material; and a recording layer formed on the switching layer and comprising magnetic particles and a nonmagnetic wall buried between the magnetic particles; the base layer, the switching layer and the recording layer being stacked to exert exchange coupling interaction, wherein structures of the base layer, the switching layer and the recording layer are set to meet the following condition: TcS less than TcB, where TcS is a Curie temperature of the switching layer, and TcB is a Curie temperature of the base layer.
The magnetic recording apparatus using the magnetic recording medium according to the fourth aspect of the present invention comprises the fourth magnetic recording medium, a heater locally heating a part of the magnetic recording medium, and a magnetic head applying a magnetic field to the magnetic recording medium.
It is preferable to perform heating and magnetic field application using the apparatus according to the fourth aspect of the present invention in a manner to meet the conditions of TcS less than TcB and 0 less than Twxe2x88x92TcS less than 100K, where Tw denotes a recording temperature of the locally heated recording layer, TcS denotes a Curie temperature of the switching layer, and TcB denotes a Curie temperature of the base layer.
According to a fifth aspect of the present invention, there is provided a magnetic recording medium, comprising a substrate; a functional layer formed on the substrate and comprising an antiferromagnetic or ferrimagnetic material; and a recording layer formed on the functional layer and comprising magnetic particles and a nonmagnetic wall buried between the magnetic particles; the functional layer and the recording layer being stacked to exert exchange coupling interaction under an ambient temperature, wherein the magnetic recording medium meets the following condition: TcR greater than TcE, where TcR is a Curie temperature of the recording layer, and TcE is a temperature at which exchange coupling interaction between the functional layer and the recording layer disappears.
The magnetic recording apparatus using the magnetic recording medium according to the fifth aspect of the present invention comprises the fifth magnetic recording medium, a heater locally heating a part of the magnetic recording medium, and a magnetic head applying a magnetic field to the magnetic recording medium.
It is preferable to perform heating and magnetic field application using the apparatus according to the fifth aspect of the present invention in a manner to meet the conditions of TcR greater than TcE and |TcExe2x88x92Tw| less than 100K, where Tw denotes a recording temperature of the locally heated recording layer, TcR denotes a Curie temperature of the recording layer, and TcE denotes a temperature at which exchange coupling interaction between the functional layer and the recording layer disappears.
According to a sixth aspect of the present invention, there is provided a magnetic recording medium, comprising a substrate; a functional layer formed on the substrate and comprising an antiferromagnetic or ferrimagnetic material; and a recording layer formed on the functional layer and comprising magnetic particles and a nonmagnetic wall buried between the magnetic particles; the functional layer and the recording layer being stacked to exert exchange coupling interaction under an ambient temperature, wherein the magnetic recording medium meets the following condition: TcR less than TcE, where TcR is a Curie temperature of the recording layer, and TcE is a temperature at which exchange coupling interaction between the functional layer and the recording layer disappears.
The magnetic recording apparatus using the magnetic recording medium according to the sixth aspect of the present invention comprises the sixth magnetic recording medium, a heater locally heating a part of the magnetic recording medium, and a magnetic head applying a magnetic field to the magnetic recording medium.
According to a seventh aspect of the present invention, there is provided a magnetic recording medium, comprising a substrate; a functional layer formed on the substrate and comprising an antiferromagnetic or ferrimagnetic material; a switching layer formed on the functional layer and comprising a magnetic material; and a recording layer formed on the switching layer and comprising magnetic particles and a nonmagnetic wall buried between the magnetic particles; the functional layer, the switching layer and the recording layer being stacked to exert exchange coupling interaction under an ambient temperature, wherein the magnetic recording medium meets the following condition: TcR greater than TcE, where TcR is a Curie temperature of the recording layer, and TcE is a temperature at which exchange coupling interaction between the switching layer and the recording layer disappears.
The magnetic recording apparatus using the magnetic recording medium according to the seventh aspect of the present invention comprises the seventh magnetic recording medium, a heater locally heating a part of the magnetic recording medium, and a magnetic head applying a magnetic field to the magnetic recording medium.
It is preferable to perform heating and magnetic field application using the apparatus according to the seventh aspect of the present invention in a manner to meet the conditions of TcR greater than TcE and |TcExe2x88x92Tw| less than 100K, where Tw denotes a recording temperature of the locally heated recording layer, TcR denotes a Curie temperature of the recording layer, and TcE denotes a temperature at which exchange coupling interaction between the functional layer and the recording layer disappears.
According to an eight aspect of the present invention, there is provided a magnetic recording medium, comprising a substrate; a functional layer formed on the substrate and comprising a magnetic material; and a recording layer formed on the functional layer and comprising magnetic particles and a nonmagnetic wall buried between the magnetic particles; the functional layer and the recording layer being stacked to exert a ferromagnetic exchange interaction under an ambient temperature, wherein the magnetic anisotropic energy density KuRL of the recording layer is not lower than 5xc3x97106 erg/cc and higher than the magnetic anisotropic energy density KuFL of the functional layer.
In the magnetic recording medium of the eighth aspect of the present invention, it is possible to use a recording layer having a multi-layered structure in which nonmagnetic layers comprising at least one element selected from the group consisting of Pt and Pd and having a thickness of not larger than 2 nm and magnetic layers are alternately stacked.
The magnetic recording apparatus using the magnetic recording medium according to the eighth aspect of the present invention comprises the eighth magnetic recording medium, and a magnetic head applying a magnetic field to the magnetic recording medium. The magnetic recording apparatus is not for performing thermally assisted magnetic recording.